The order for the Do-F night bomber (later the Do 11) was raised by the Reichsverkehrministerium (RVM) as a cargo and postal aircraft. The first flight of this twin-engined shoulder-wing aircraft, produced at Altenrhein, took place on 7 May 1932. After several test flights for the Reichsverband der deutschen Luftfahrtindustrie (RdL), it underwent technical and tactical testing at Lipetsk the same year. As the first bomber, it was intended to carry the new se bombs, and it could take either six vertically-mounted magazines containing a total of 30 50kg bombs, or 120 10kg bombs on a special type of bomb rack. So many problems were experienced with the retractable undercarriage of the Do 11 that the designers later reverted to a fixed undercarriage. This aircraft, designated Do II in its military form, was satisfactory as far as power was concerned, but suffered from poor flying qualities. Moreover, the manually assembled airframe was found to be too weak, which resulted in wing vibration and fuselage deformation. From 1932 mass production of the Do 11 C began at Friedrichshafen, with Siemens Sh 22 B-2 engines replacing the Siemens Jupiter VI. This variant served mainly as a trainer for bomber crews, and had covered gun positions and no glazing in the nose. The Do 11 D had a retractable undercarriage, a new type of rudder control, and additional fins under the tailplane. Reducing the span from 28m to 26.3m failed to alleviate wing vibration because the problem lay in the weak fuselage. Of 150 ordered only 76 were delivered.